Turn top-library comment into non-dartdoc. (#1290)

* Turn top-library comment into non-dartdoc.

Prepare for lints 3.0.0, which reports this as a dangling library comment, when it's probably just not intended a doc comment at all.

* Update lib/src/debug.dart

Keep as doc-comment, adding the then required `library;` to sit on.

Co-authored-by: Nate Bosch <[email protected]>

---------

Co-authored-by: Nate Bosch <[email protected]>

Author: lrhn

lib/src/debug.dart

@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /// Internal debugging utilities.
+library;
+
 import 'dart:math' as math;
 
 import 'chunk.dart';